Polycrystalline diamond (PCD) materials and PCD elements formed therefrom are well known in the art. Conventional PCD is formed by combining synthetic diamond grains with a suitable solvent catalyst material to form a mixture. The mixture is subjected to processing conditions of extremely high pressure/high temperature, where the solvent catalyst material promotes desired intercrystalline diamond-to-diamond bonding between the grains, thereby forming a PCD structure. The resulting PCD structure produces enhanced properties of wear resistance and hardness, making PCD materials extremely useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired.
Solvent catalyst materials typically used for forming conventional PCD include metals from Group VIII of the Periodic table, with cobalt (Co) being the most common. Conventional PCD can comprise from 85 to 95% by volume diamond and a remaining amount solvent catalyst material. The material microstructure of conventional PCD comprises regions of intercrystalline bonded diamond with solvent catalyst material attached to the diamond and/or disposed within interstices or interstitial regions that exist between the intercrystalline bonded diamond regions.
A problem known to exist with such conventional PCD materials is that they are vulnerable to thermal degradation, when exposed to elevated temperature cutting and/or wear applications, caused by the differential that exists between the thermal expansion characteristics of the interstitial solvent metal catalyst material and the thermal expansion characteristics of the intercrystalline bonded diamond. Such differential thermal expansion is known to occur at temperatures of about 400° C., can cause ruptures to occur in the diamond-to-diamond bonding, and eventually result in the formation of cracks and chips in the PCD structure, rendering the PCD structure unsuited for further use.
Another form of thermal degradation known to exist with conventional PCD materials is one that is also related to the presence of the solvent metal catalyst in the interstitial regions and the adherence of the solvent metal catalyst to the diamond crystals. Specifically, the solvent metal catalyst is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of the PCD material to about 750° C.
Attempts at addressing such unwanted forms of thermal degradation in conventional PCD materials are known in the art. Generally, these attempts have focused on the formation of a PCD body having an improved degree of thermal stability when compared to the conventional PCD materials discussed above. One known technique of producing a PCD body having improved thermal stability involves, after forming the PCD body, removing all or a portion of the solvent catalyst material therefrom.
For example, U.S. Pat. No. 6,544,308 discloses a PCD element having improved wear resistance comprising a diamond matrix body that is integrally bonded to a metallic substrate. While the diamond matrix body is formed using a catalyzing material during high temperature/high pressure processing, the diamond matrix body is subsequently treated to render a region extending from a working surface to a depth of at least about 0.1 mm substantially free of the catalyzing material, wherein 0.1 mm is described as being the critical depletion depth.
Japanese Published Patent Application 59-219500 discloses a diamond sintered body joined together with a cemented tungsten carbide base formed by high temperature/high pressure process, wherein the diamond sintered body comprises diamond and a ferrous metal binding phase. Subsequent to the formation of the diamond sintered body, a majority of the ferrous metal binding phase is removed from an area of at least 0.2 mm from a surface layer of the diamond sintered body.
In addition to the above-identified references that disclose treatment of the PCD body to improve the thermal stability by removing the catalyzing material from a region of the diamond body extending a minimum distance from the diamond body surface, there are other known references that disclose the practice of removing the catalyzing material from the entire PCD body. While this approach produces an entire PCD body that is substantially free of the solvent catalyst material, is it fairly time consuming. Additionally, a problem known to exist with this approach is that the lack of solvent metal catalyst within the PCD body precludes the subsequent attachment of a metallic substrate to the PCD body by solvent catalyst infiltration.
Additionally, PCD bodies rendered thermally stable by removing substantially all of the catalyzing material from the entire body have a coefficient of thermal expansion that is sufficiently different from that of conventional substrate materials (such as WC—Co and the like) that are typically infiltrated or otherwise attached to the PCD body. The attachment of such substrates to the PCD body is highly desired to provide a PCD compact that can be readily adapted for use in many desirable applications. However, the difference in thermal expansion between the thermally stable PCD body and the substrate, and the poor wetability of the thermally stable PCD body diamond surface due to the substantial absence of solvent metal catalyst, makes it very difficult to bond the thermally stable PCD body to conventionally used substrates. Accordingly, such PCD bodies must be attached or mounted directly to a device for use, i.e., without the presence of an adjoining substrate.
Since such PCD bodies, rendered thermally stable by having the catalyzing material removed from the entire diamond body, are devoid of a metallic substrate they cannot (e.g., when configured for use as a drill bit cutter) be attached to a drill bit by conventional brazing process. The use of such thermally stable PCD body in this particular application necessitates that the PCD body itself be mounted to the drill bit by mechanical or interference fit during manufacturing of the drill bit, which is labor intensive, time consuming, and does not provide a most secure method of attachment.
While these above-noted known approaches provide insight into diamond bonded constructions capable of providing some improved degree of thermal stability when compared to conventional PCD constructions, it is believed that further improvements in thermal stability for PCD materials useful for desired cutting and wear applications can be obtained according to different approaches that are both capable of minimizing the amount of time and effort necessary to achieve the same, and that permit formation of a thermally stable PCD construction comprising a desired substrate bonded thereto to facilitate attachment of the construction with a desired application device.
It is, therefore, desired that diamond compact constructions be developed that include a PCD body having an improved degree of thermal stability when compared to conventional PCD materials, and that include a substrate material bonded to the PCD body to facilitate attachment of the resulting thermally stable compact construction to an application device by conventional method such as welding or brazing and the like. It is further desired that such a compact construction provide a desired degree of thermal stability in a manner that can be manufactured at reasonable cost without requiring excessive manufacturing times and without the use of exotic materials or techniques.